1 AP Chemistry Chapter 21 - The Nucleus: A Chemist?s View 21.1 Nuclear Stability and Radioactive Decay A. Radioactive Decay 1. Decomposition forming a different nucleus and producing one or more particles a. Total mass number and atomic number must be conserved in any nuclear change nCHeBe 101264294 +?+ B. Zone of Stability 1. Of 2000 known nuclides, only 279 are stable with respect to radioactive decay 2. All nuclides with more than 83 protons (bismuth) are unstable 3. Light nuclides are most stable when the neutron/proton ratio is 1 4. Heavier nuclides are most stable when the neutron/proton ratio is greater than 1 5. Magic numbers a. Special stability exists when the number of protons or neutrons is: 2, 8, 20, 28, 50, 82, 126 C. Types of Radioactive Decay